This invention relates to magnetic separation in general and more particularly to a device for high gradient magnetic separation of magnetizable particles from a flowing medium.
A device for separation of magnetic particles from a flowing medium with an ordered filter structure which contains, between the ends of two pole pieces of a magnet device, in a magnetic field of predetermined magnetic field strength directed substantially parallel or antiparallel to the flow direction of the medium, parts of magnetic material of predetermined coercitive field strength H.sub.c, which are arranged at least approximately perpendicular to the direction of the magnetic field, is described in DE-OS 26 28 095.
In magnetic separation methods, the fact that, in a sufficiently strong magnetic field, a magnetizable particle is subjected to a force which moves or holds it against other forces acting on it such as the force of gravity or against hydrodynamic friction forces occurring in a liquid medium, is utilized. Such separation methods can be provided, for instance, for steam or cooling water loops in conventional as well as in nuclear power stations. In the liquid or gaseous medium of these loops, particles, which have generally been produced by corrosion, are suspended. These particles are in part ferromagnetic such as magnetite (Fe.sub.3 O.sub.4), partly antiferromagnetic such as hematite (.alpha.-Fe.sub.2 O.sub.3) or paramagnetic such as copper oxide (CuO). These particles, which, in addition, generally appear in different sizes, are therefore differently magnetizable.
Methods and apparatus are known, by means of which even very small particles with diameters in the micrometer range can be filtered magnetically from a flowing medium with a fairly large degree of separation. These methods work with high magnetic fields and, in particular, with very high field gradients. One therefore also speaks of high-gradient magnetic separation. A corresponding separating device is the device described in the above-mentioned DE-OS 26 28 095. It contains an ordered filter structure consisting of a multiplicity of wire screens which are arranged closely one behind the other to form a stack and are arranged perpendicular to the flow direction of the medium in a relatively strong magnetic field which, in the region of the filter structure, is directed, parallel or antiparallel to the direction of the medium and causes there, for instance, a magnetic flux density of at least 0.7 Tesla. The wires consist of a non-corroding ferromagnetic material such as alloy steel and their gauge is very small, for instance, less than 0.1 mm. The wires are magnetized to saturation and the flux density gradients, which may be up to 10.sup.3 Tesla/cm, are then large enough so that even weakly magnetizable particles can be filtered out of the flowing medium with a relatively large degree of separation.
In such devices for high gradient magnetic separation, strong electromagnets are generally required for magnetizing and, thus, for producing the high flux density gradient, because of the relatively large demagnetization factor of the wires, which may be, for instance, 0.5. Then, however, correspondingly large amounts of conductor material, for instance, of copper, and also, in general, much ferromagnetic material, in the form of yokes and pole pieces for conducting the magnetic flux, must be provided. These magnetic devices are therefore accordingly expensive and also generally consume much energy. The investment and operating costs of such a device for high gradient magnetic separation are therefore relatively high.
It is an object of the present invention to improve the device mentioned at the outset in such a manner that the costs for procuring as well as for operating such magnetic apparatus are reduced in comparison with the known separation devices.